ABSTRACT Using function-based structure models and alanine scanning, we have identified a potentially general mode for phospho-amino acid- and context sequence-binding by IgG and scFv Abs. We propose to exploit this phenomenon to design a phospho-focused scFv library in which the phospho-amino acid binding hypervariable complementarity determining region (CDR) H2 of the Ab is held constant while sequences along the protein- and peptide-binding groove composed of the other 5 CDRs are mutated to accommodate various context sequences. This phospho- focused library will be used to both bias- and direct the binding of Abs to a specific appropriately modified amino acid on a peptide based on surface loops near enzyme active site. The Abs will be affinity matured against non-phosphorylated peptide and/or full length protein. The matured Abs will be tested for their ability to act as steric inhibitors to the enzyme to which they were designed. If successful, our system will enable the rapid generation of reversible inhibitors with utility in biochemistry and pharmacology.